In recent years, digital printing has offered new possibilities in the flooring industry to customize decorative patterns for flooring applications.
Instead of printing large quantities of decor paper with a decorative pattern by rotogravure or direct printing, digital printing offers a possibility to print small quantities of decor paper. Thereby, the digital printing technique offers a possibility to create a large number of different patterns and to customize patterns.
Digital printing has been used to form decorative patterns for laminate floorings but also on wooden floorings in order to form a fantasy pattern on the surface or to print a natural wood pattern.
By digital printing is conventionally meant printing by means of non-contact printing, for example using a Drop-on-Demand (DOD) technique. A drop of ink is placed with great accuracy on a paper or wood surface. Examples of DOD techniques are piezoelectric DOD inkjet and thermal DOD inkjet. In a piezoelectric DOD inkjet printer, the piezoelectric material changes shape when a voltage is applied. The change of shape of the piezoelectric material generates a pressure pulse in the fluid, thereby ejecting a droplet of ink from the nozzle. In a thermal DOD inkjet printer, ink drops are ejected by forming an ink vapour bubble by heating the ink.
When printing on a wooden surface, a UV curable ink is conventionally used. The UV curable ink comprises a UV curable polymer. The UV curable ink is applied on the wooden surface by means of digital printing. The ink is exposed to strong UV light such that the UV curable polymer cures. Thereby, by curing the polymer, the ink is no longer wet after the printing process and can therefore no longer come off.
An advantage of UV curable inks is that it may be applied to a wide range of substrates without any need for coating the substrate before printing due to the ink is cured directly after printing. This property is especially advantageous when printing on a wooden surface. The UV curable ink is cured before any bleeding of the ink into the wood has occurred.
However, UV curable inks are expensive compared to another types of inks. Furthermore, UV curable inks are generally not environmentally friendly, mainly due to the UV curable polymers included in the ink. Special consideration has to be taken during curing in order to avoid exposure to vapours formed by curing and also to avoid exposure to UV radiation originating from the UV lamp used for curing. Before being cured, UV curable inks may be extremely irritating to eyes and skin. Since UV curable inks do not dry without being cured, it remains wet until being cured. Consequently, the risk of skin irritation remains until the UV curable ink has been washed off. If a person is exposed to UV curable inks or vapours originating from UV inks during a long time, the exposure may cause sensitization, i.e. that even low level exposure may lead to a violent reaction.